The present invention relates to a motion platform and in particular, to a method and apparatus incorporating a motion platform to test shoes.
Motion platforms are devices that can move an object through an arbitrary trajectory in 3 dimensional space within a given working volume while maintaining precise control over the position, velocity and acceleration of the object. One type of mechanism that is suitable for creating a general-purpose motion platform is a Stewart platform or hexapod. Stewart platforms are well-known and include a parallel linkage that permits movement with 6 degrees of freedom: independent and simultaneous translation and rotation about and along each of the three primary Cartesian axes X, Y and Z. A Stewart platform includes six xe2x80x9clegsxe2x80x9d each of which is extendible to translate and rotate a platform about all three Cartesian axes. In general, Stewart platforms are known for their low mass, high mechanical stiffness and large payload capacities.
Typically, Stewart platforms have extendible xe2x80x9clegsxe2x80x9d which are hydraulic, pneumatic, lead screw electric or ball screw electric actuators and are used in automated assembly lines. Examples of automatic assembly machines using a Stewart platform are disclosed in U.S. Pat. Nos. 6,041,500 and 5,987,726. These prior art Stewart platforms generate tremendous thrust, particularly hydraulically actuated platforms, at the expense of velocity and are limited to accuracy in the range of one to two millimeters.
In many applications, it is desirable to generate platform velocities of greater than 2.5 meters per second and up to 3 m/s or more, with accuracy in the sub-millimeters range and maintain thrust in the range of 1000 pounds. Further it would be desirable if such a platform could also deliver vertical acceleration in excess of 3 g and rotation rates of up to 1000 degrees per second. One such application is footwear testing.
It is desirable to determine the effect of shoe design on foot motion and impact control, particularly for athletic footwear. Athletic footwear manufacturers typically evaluate human subjects wearing test shoes during prescribed movements. These human tests are time-consuming, unreliable and fail to reveal internal motion or forces within the ankle or leg, apart from subjective observations by the test subject, which are inherently unreliable.
Robotic footwear testers have been directed at simulating walking or running motions. One example is the tester disclosed in U.S. Pat. No. 4,130,007. The difficulty with such robotic testers is that they are mechanically complex yet only very simple walking or running motions may be simulated and they cannot accurately simulate complex motions. As a result, only very limited test information is obtained.
Therefore, there is a need in the art for methods and apparatuses to robotically test footwear which may incorporate a novel motion platform.
The present invention is directed to a novel motion platform falling within the generic category of Stewart platforms or hexapods. In particular, the motion platform of the present invention is incorporated into a novel apparatus and method for testing footwear.
Therefore, in one aspect, the invention comprises a motion platform comprising a base, a platform, a motion controller and at least 6 linear actuating mechanisms disposed between and connected to the base and the platform, wherein each actuating mechanism comprises an electromagnetic linear actuator comprising an electric thrust block and a magnetic thrust rod and each actuating mechanism is controlled by the motion controller.
In another aspect, the invention may comprise a shoe testing apparatus comprising:
(a) a fixed artificial foot including a force sensor, for wearing the shoe;
(b) a motion platform capable of moving and being controlled with 6 degrees of freedom;
(c) means for actuating the motion platform and striking the shoe with the platform in a manner simulating the running or walking gait of a shoe wearer;
(d) means for recording the forces sensed and transmitted by the force sensor.
In another aspect, the invention may comprise a method of testing a shoe, comprising the steps of:
(a) fitting an artificial foot within the shoe, providing a force sensor attached to the artificial foot and fixing the foot and shoe in position;
(b) providing a motion platform capable of moving and being controlled in 6 degrees of freedom;
(c) providing a foot trajectory and transforming the foot trajectory to a platform trajectory;
(d) actuating the motion platform with the platform trajectory to strike the shoe; and
(e) recording the resulting forces with the force sensor.